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29 Mar 2010, 13:58

Gmat Prep says the answer is C, but I think it is A. Can someone tell me what I am doing wrong?

1. x is negative

So, let x be -1. 1 ^ 2 * - * -3 = 31 ^ 3 * - * -3 = 3

If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.

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01 Apr 2010, 13:01

gmatready7 wrote:

Gmat Prep says the answer is C, but I think it is A. Can someone

If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.

I think it's an issue of order of operations. Exponents come before multiplication so if x = -1 and n is even say 2Then -3 * -1^2 = -3 * 1 = -3

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01 Apr 2010, 14:00

PeterFaulkner wrote:

gmatready7 wrote:

Gmat Prep says the answer is C, but I think it is A. Can someone

If x is negative the answer is always positive. If the problem were -3(x)^n then that answer would be C. However, without the brackets you must distribute the negative after you take x^n...therefore the answer will always be a negative number multiplied by -3 which gives a positive answer.

I think it's an issue of order of operations. Exponents come before multiplication so if x = -1 and n is even say 2Then -3 * -1^2 = -3 * 1 = -3

x = -1 and n is odd say 3then -3 * -1^3 = -3 * -1 = 3

so A by itself is insufficient....Please correct me if I am wrong

But you can raise a negative number to an even power and the answer is still negative. -1^2 = -1. For it to be positive you must use brackets around the -1....(-1)^2 = 1. This is why I chose answer a. Are we to assume there are brackets on the GMAT even though they are not shown?

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Hi,what does the sign of -3x^n depends on ...1) sign of x..2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..

lets see the statements..(1) x is negative.we are told of one of the two things required .. insuff

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17 Jan 2016, 06:51

chetan2u wrote:

NoHalfMeasures wrote:

If n is an integer, is -3x^n positive?(1) x is negative.(2) n is odd.

pls press kudos if you liked the question

Hi,what does the sign of -3x^n depends on ...1) sign of x..2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..

lets see the statements..(1) x is negative.we are told of one of the two things required .. insuff

(2) n is odd.we are told of one of the two things required .. insuff

combined both the info is provided ... suff

I don't understand -- if x is negative then -3(x) = positive number and -3x^n will be positive -- is it for PEMDAS?

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Hi,what does the sign of -3x^n depends on ...1) sign of x..2) value(odd/even) of n, and not on sign of n, as it will turn the x variable in a fraction but will not effect the sign of that fraction or integer..

lets see the statements..(1) x is negative.we are told of one of the two things required .. insuff

(2) n is odd.we are told of one of the two things required .. insuff

combined both the info is provided ... suff

I don't understand -- if x is negative then -3(x) = positive number and -3x^n will be positive -- is it for PEMDAS?

That x^n operation must come first?

Hi,x^n operation is not there in PEMDAS..because x^n is one number..example 4=2^2 so if we have 7*2^2, it means 7*4, because 2^2 is one number..same goes for x^n..hence even sign of n is important..because power of an even number will make any number positive, even if it is negative..say x=-2 and n=2..(-2)^2=-2*-2=4, whereas -2^3=-2*-2*-2=-8, a -ive number..hope it helps
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07 Oct 2016, 22:01

ninomoi wrote:

If n is an integer, is -3x^n positive?

1. x is negative2. n is odd

pls explain. Thanks

Answer should be C

For the given statement to be positive x should be negative and n should be odd numberSt 1 :states that x is negative but we dont know if n is even or odd if n is even insuff if n is odd sufficient so st 1 is insuffSt 2:States that n is odd again we dont know the value of x whether positive or negative if positive answer to question is no if negative answer to ques is yes again insuff

Combined sufficient since n is odd and x is negative statement will be positive.